Conventional X-ray tube apparatus include an enclosure rotation type X-ray tube apparatus in which an anode rotates together with an enclosure, and an electron beam from an electron source of a cathode provided about an axis in the X-ray tube is focused and deflected by a magnetic field generator provided out of the X-ray tube to form a focal spot in a predetermined position on a target disk of the anode (see, for example, patent document 1). The magnetic field generator of this type provided in the enclosure rotation type X-ray tube apparatus is formed of a coil and yoke. The generator generates a focusing magnetic field for focusing an electron beam, and may also generate a deflection magnetic field superimposed thereon for deflecting the electron beam. Such magnetic field generators include, for instance, a quadrupole magnetic field lens and an octupole magnetic field lens. Accordingly, the electron beam may be focused and deflected to form a focal spot in a predetermined position on the target disk of the anode. Moreover, rotation of the anode will avoid concentrated collision of the focused and deflected electron beam in a same position on the target disk. Consequently, heat generated due to collision of the electron beam will not be concentrated in the same position on the target disk, leading to prevention of the target disk from being molten. Furthermore, the heat generated due to the collision of the electron beam is dissipated from the target integrated into the enclosure out of the X-ray tube through heat conduction, which may realize an improved cooling efficiency in the X-ray tube and successive irradiation with X-rays without any necessity of a cooling time.    [Patent Document 1]    U.S. Pat. No. 5,883,936